Hybrid active focusing with adaptive dispersion for higher defect sensitivity in guided wave inspection of cylindrical structures

Abstract

Ultrasonic guided wave inspection is widely used for scanning prismatic structures such as pipes for metal loss. Recent research has investigated focusing the sound energy into predetermined regions of a pipe in order to enhance the defect sensitivity. This paper presents an active focusing technique which is based on a combination of numerical simulation and time reversal concept. The proposed technique is empirically validated using a 3D laser vibrometry measurement of the focal spot. The defect sensitivity of the proposed technique is compared with conventional active focusing, time reversal focusing and synthetic focusing through an empirically validated finite element parametric study. Based on the results, the proposed technique achieves approximately 10 dB improvement of signal-to-coherent-noise ratio compared to the conventional active focusing and time reversal focusing. It is also demonstrated that the proposed technique to have an amplitude gain of around 5 dB over synthetic focusing for defects <0.5λ_s. The proposed technique is shown to have the potential to improve the reliably detectable flaw size in guided wave inspection from 9% to less than 1% cross-sectional area loss.

Keywords:

• Ultrasonic guided waves
• active focusing
• defect sensitivity
• finite element analysis
• pipe inspection

Acknowledgement

The authors gratefully acknowledge TWI Ltd and the Center for Electronic System Research (CESR) of Brunel University for providing the funding that made this study possible. The authors are also grateful to Prof. P. Cawley of Imperial College, London Prof. W. Balachandran of Brunel University, London and Prof. P. Mudge of Plant Integrity Ltd., for their constructive inputs and many useful discussions.

Disclosure statement

No potential conflict of interest was reported by the authors.